Tap for rolling internal threads



Dec. 25, 1962 P. A. KOEHLER 3,069,940

TAP FoR ROLLING INTERNAL THREADS Filed Nov. 9, 1959 3/\ 27@ 25 "A W 24 uw /7 az! .la/l: 1 2 Z Fig. 3

Fig. 4

f7 Tram/5y States Fatentttitice Fatertted 25, i952 @69,946 TAP FR MELUN@LQTERNAL THREADS Paul A. Koehler, Edsal Drive, Lyndhurst, hio; MarianElizabeth Koehler, executrx of said Paul A. Koehler, decease- Fiied Nov.9, 195?, Ser. No. 851,804 ll Qlalrn. (Cl. Sti- 6) This invention relatesto taps for rolling internal threads.

Although there have been prior attempts to provide taps for rollinginternal threads, such taps are not in widespread use despite the factthat rolled threads are stronger and smoother than cut threads.

One of the principal reasons Why such prior taps have not achievedgeneral commercial acceptance is that the designs have been such as tobe unable to provide suicient rigidity for the thread forming rolls towithstand the side loads imposed thereon without deecting, resulting ininaccurate and non-uniform sizing of the thread.

According y, it is an object of the present invention to provide a tapfor rolling internal threads in which the holder for the thread formingrolls is so constructed as to rigidly support the thread forming rollsagainst deflection under side loads thereon.

It is another object to provide a tap of the type described in which aone piece holder supports the thread forming rolls at both ends thereoffor maximum rigidity against deflection of such rolls.

lt is another object to provide an internal thread rolling tap with aplurality of thread forming rolls and with a simple means for adjustingthe relative radial position of one thread forming roll with respect toanother for accurately contro-lling the size of the thread to be formedin a workpiece.

It is another object to provide a tap for rolling internal threads inwhich the holder for the thread forming rolls is one-piece for maximumrigidity and has recesses for containing the thread forming rolls whichare easy to machine.

It is another object to provide a tap of the type described in which thethread forming rolls have shafts integral therewith and the holder hasroll supporting portions having radially outward openings through whichthe shafts may be inserted, thus permitting the shafts to be integralwith the rolls and the roll supporting portions be integral with theholder for maximum rigidity.

Other objects will become apparent from the drawings and from thefollowing description in which:

FIG. l is a side view of the tap.

FIG. 2 is an end View,

FIG. 3 is a one quarter section view along the lines 3--3 of FIG. 2 andshowing a work piece with the tap. FIG. 4 is a side View of a modifiedform of the tap.

FiG. 5 is an end view of the modified form.

FIG. 6 is a one quarter section view along the lines 6-6 of FIG. 5.

FIG. 7 is a section along the lines 7-7 of FIG. 6.

The form of the tap shown in FIGS. l-3 includes a holder 10 which has ashank lll at one end adapted to be received and clamped in a suitablechuck, not shown. The other end of the holder includes axially spacedthread forming roll supporting portions l2 and 13 which are integralwith the holder and which have a plurality of recesses i4 therebetween,the recesses being radially spaced from the longitudinal axis of theholder and being angularly spaced from each other. The roll supportingportions l2 and i3 are integral with an axially extending portion 17which contains the recesses 14. This axial extending portio-n 17traverses the axis of the holder and extends radially between therecesses.

The roll supporting portions l2 and .i3 each have a plurality ofradially outward front and rear openings l5 and 16 on each side of therecesses i4. The bottoms of the openings l5 and 16 provide bearingsurfaces l and 19 which are radially spaced from the axis of the holderand angularly spaced from each other. The bearing surfaces 13 and 19 arein axial alignment with the respective recesses la.

Mounted in each of the recesses la is a. thread forming roll 22 having aseries of annular thread forming ribs 23 thereupon. Each roll has shaftextensions 24 and 25 extending from opposite sides thereof andconstituting mounting means which is engageable with the bearingsurfaces 18 and i9 for rotatably supporting the roll. rl`he shaftextension 25 has a groove 2'? formed therein and there is a split ring23 which ts Within an annular groove 29 in the holder and within thegroove 27 of each roll for retaining the rolls in the recesses la. nthesplit ring 2S preferably does not extend radially beyond the peripheryof the holder 1l.

The thread forming ribs 23 project radially from the recesses ltbut theshaft extensions Z4- and 2 are preferably within the radial contines ofthe holder The recesses ltd and the openings l5 and le are so formed inthe holder that their comon longitudinal axis 3l is parallel to the axis32 of the holder when viewed as in FIG. 3 and is at an angle 33 to theaxis 32 when viewed as in FIG. 1. The angle 33 corresponds to the helixangle of the thread to be rolled in a workpiece. The end surfaces ofeach recess l@ are normal to the respective axis 31.

When rolling the thread, the tap ttl is rotated relative to theworkpiece, the latter being shown at 2@ in FIG. 2. As the tap enters theworkpiece and rolls the thread therein, extremely high pressure isexerted in a radially inward direction upon the rolls. ln order that thethreads in the workpiece be accurately formed with a uniform pitchdiameter, it is necessary that the rolls 22 be rigidly supported againstradially inward detlection due to such inward pressure. Maximum supportfor such rolls is obtained by making the roll supporting portions l?.and 13 integral with each other and with the holder lt), and by havingsuch portions of continuous transverse cross section.

The axially extending portion ll7 between the roll suporting portions l2and i3 is provided with a maximum of cross section by making the rolls22 of a relatively small diameter with the recesses le fitting closelythereabout so that a substantial thickness of metal is provided at thecentral portion of the axially extending portion 17 as well as betweenthe recesses lil.

To facilitate the making of a one-piece holder for the thread formingrolls, the openings l5 and ld are open to the periphery of the rollsupporting portions l2. and This permits accurate milling of therecesses Sirtand openings 15 and le by conventional means. Having theopenings and lo open to the radial periphery of the holder also permitsthe rollers 22 to be integral with their shafts 2li- 25 since therollers can be assembled to the holder by lateral insertion into therecesses la and the openings 15 and lo.

An optional form of the holder is shown in FlGS. 4 through 7. In thisform, the holder itl has a shank 4l at one end and at the other end hasroll supporting portions a?. and 43 which are spaced from each other butwhich are integrally connected with the holder by means of an axiallyextending portion all. The latter has a pair of recesses l5 formedtherein for receiving thread forming rolls d6. In this instance only tworolls 46 are illustrated but it is understood that in both forms of theinvention the number of rolls employed s optional.

fa c d In the modiied form, the roll supporting portions 42 and 43 havebores 49 and 59 formed on opposite sides of each recess 4.5 and axialiyaligned therewith. The bores 49 and 50 form bearing surfaces for pins 53therein upon which the rolls 46 are mounted. 1n addition, the bores 54Bextend to the opposite end of the holder.

Each set of bores 49-53 and recesses 45 have a cornrnon longitudinalaxis S7 which is parallel to the 1ongitudinal axis of the holder in oneplane, as viewed in FIG. 6, and which is at an angle .39 to the axis 55when viewed in another plane which is at right angles to the rstmentioned plane, as shown in FiG. 2.

The end surfaces or the recesses 45' are normal to the respective axis57. Bore 49 is of larger diameter but concentric with bore di?. Mountedin each set of bores i9 and 50 are pins 53. pin :53 has concentriccyiindrical end portions o2 and and an intermediate cylindrical portion64 whose axis is parallel to but oitset from the axis of the endportions so that the cylindrical portion 64 is eccentric to thecylindrical portions 62 and 63.

The thread forming rolls are mounted on the intermediate portions d4 ofthe pins and have a close rotating tit thereon. Since the intermediateportions 64 of the pins are eccentric with the end portions 62 and 63,rotation of the pin within the pin supporting bores 49 and 50 will causethe roll 46 which is mounted on the pin being rotated to assume variousadjusted lateral positions with respect to the other roil 45. By thismeans, the pitch diameter of the thread being rolled into the workpiecemay be adjustably varied. When the pins 53 have been rotated to theirproper setting, they are clamped in such rotated position by set screws70 threaded into the holder 40. The set screws also prevent end wisedisplacement of the pins S3. As is evident from the drawings, set screws70 do not project beyond the periphery of holder 4@ and thus are withina circle circumscribed by the rolls 46 when holder 40 is rotated on itsiongitudinal axis. Shaft 53 is accessible from the front end of theholder for rotating the same for adjusting the lateral positions of therolls with respect to each other, a screw driver slot being provided inthe outer end of the shaft for this purpose.

This form ot the invention likewise provides a very rigid supportagainst radially inward defiection of the rolls due to pressure of thesame against the workpiece. Such very rigid support is brought about bythe tact that the roll supporting portions 42 and 43 are integral withthe holder and are connected by an axially extending portion which is otmaximum cross sectional and which is integral with the portions 42 and43.

Although two embodiments of the invention have been *2 shown anddescribed, it is apparent that various other changes or modications maybe made without departing from the scope of the invention as defined inthe following claims.

I claim:

A tap for roll forming internal threads in a workpiece, said tapincluding a holder and at least a pair of thread forming rolls spacedtransversely on said holder and each having an annular thread formingrib thereon, said holder having front and rear sections having openingsforming iront and rear bearing portions for each roll for rotatablysupporting the same with the axis of rotation being generallylongitudinal of said holder, said front section being integral with saidholder and being irnperforate except or said openings therein forrigidly supporting the front ends of said rolls against radial inwarddeiiection, said rear section also being integral with said holder andimperforate except for the openings therein for rigidly supporting therear ends of said rolls against radial inward deection, said sectionsbeing on opposite ends of said rolls and being joined by an axiallyextending portion integral therewith and which traverses the axis ofsaid holder and which surrounds a substantial portion of each of saidrolls, said rolls having shafts extending frorn each end thereofjournaled in said bearing portions, said front bearing portions beinglocated at the extreme front end of said holder, and all of saidopenings extending radially to the periphery of said sections wherebysaid shafts may be inserted radially into said openings.

References Cited in the le of this patent UNITEB STATES PATENTS 490,628Heckert Een. 24, 1893 859,644 Cummings July 9, 1907 885,068 Moy et alApr. 2l, 1908 1,785,905 Kerruish Dec. 23, 1930 2,331,757 Anders Got. 12,1943 2,349,863 Hallberg May 30, 1944 2,645,954 Pfingsten July 21, 19532,828,493 Koehler Apr. 1, 1958 FOREIGN PATENTS 506,884 Great BritainJune 6, 1939 538,222 Canada Mar. 12, 1957 659,313 Great Britain Oct. 24,1951 17,005 Great Britain Aug. 6, 1898 872,103 France Ian. 29, 1942749,772 Germany Dec. 4, 1944 V5116lb/7f Germany Feb. 2, 1956 1,185,915France Feb. 16, 1959

